In electronic circuits, energy is not only consumed — it can also be temporarily stored and released when needed. One of the most important components that makes this possible is the capacitor.
In this blog, we’ll understand what a capacitor is, how it works, how it stores energy, and what capacitance really means.
⚙️ What is a Capacitor?
A capacitor is an electronic component that stores electrical energy in the form of an electric field.
🧩 Structure — How It’s Made
A basic capacitor consists of three parts:
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Two Conducting Plates – usually made of metal like aluminum or copper.
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Dielectric Material – an insulating layer placed between the plates (air, paper, plastic, ceramic, or mica).
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Leads / Terminals – used to connect the capacitor into a circuit.
So physically, a capacitor looks like two metal plates separated by a thin insulating film.
The dielectric does not conduct electricity — it helps store charge by preventing electrons from jumping directly from one plate to the other.
⚡ How Does a Capacitor Work?
Before applying voltage:
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Both plates are electrically neutral, meaning they have an equal number of positive and negative charges.
After connecting the capacitor to a battery:
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The negative terminal of the battery pushes electrons toward the bottom plate of the capacitor through the connecting wire.
→ This bottom plate starts accumulating extra electrons and becomes negatively charged. -
As electrons pile up on the bottom plate, they repel electrons from the top plate (because like charges repel).
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These repelled electrons from the top plate move through the external circuit toward the positive terminal of the battery, which is electron-deficient and attracts them.
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The top plate, having lost electrons, becomes positively charged.
Meanwhile, the dielectric between the plates prevents direct electron flow — it only allows an electric field to form.
As charge separation builds up, a potential difference (voltage) develops across the plates.
This continues until the voltage across the capacitor equals the battery voltage — at that point, charging stops.
The electric field created between the plates stores the electrical energy.
The electric field strength is given by:
E = V / d
where:
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V = voltage across the plates
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d = distance between the plates
🔋 Energy Storage in a Capacitor
The capacitor now holds energy in the electric field between its plates.
If the battery is disconnected, the charges remain stored — the capacitor stays charged.
It releases this stored energy only when a conductive path (like a resistor or load) is connected between its plates.
Electrons then flow from the negatively charged plate to the positively charged plate through the external circuit, producing current until both plates become neutral again.
This process is called discharging the capacitor.
🧮 What is Capacitance?
Capacitance is the ability of a capacitor to store electric charge per unit voltage.
In simple terms, it tells how much charge a capacitor can store for a given applied voltage.
Mathematically:
C = Q / V
where:
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C = capacitance (Farads, F)
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Q = charge stored (Coulombs)
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V = voltage across the capacitor (Volts)
A higher capacitance means greater charge storage capability.
⚡ Current–Voltage Relationship in a Capacitor
The relationship between current and voltage for a capacitor is:
I = C (dV/dt)
This means:
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If voltage changes rapidly, current is large.
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If voltage is constant, current is zero.
So a capacitor allows current to flow only when voltage is changing.
A capacitor opposes sudden changes in voltage.
🧠 Factors Affecting Capacitance
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Area of Plates (A): Larger area → more charge → higher capacitance
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Distance Between Plates (d): Greater distance → lower capacitance
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Dielectric Constant (ε): Better dielectric → higher capacitance
For a parallel plate capacitor:
C = ε (A / d)
From this:
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Bigger plates → higher capacitance
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Closer plates → higher capacitance
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Better dielectric → higher capacitance
🔥 Energy Stored in a Capacitor
The energy stored in a capacitor is given by:
E = (1/2) C V²
🔚 Conclusion
A capacitor is a fundamental electronic component that stores electrical energy in the form of an electric field. By separating charge across two plates using a dielectric, it plays a crucial role in energy storage, voltage stabilization, filtering, timing circuits, and signal coupling.
Capacitance defines how effectively a capacitor can store charge, and it depends on the physical structure and dielectric material used. Capacitors respond to changes in voltage rather than steady values, which makes them essential in both analog and digital electronics.
Understanding capacitors and capacitance lays a strong foundation for learning RC circuits, filters, power supplies, and advanced analog electronic systems.
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